The present invention relates to a variable compression ratio mechanism of a reciprocating internal combustion engine, and particularly to a variable compression ratio mechanism of a reciprocating piston engine capable of varying the top dead center (TDC) position of a piston by means of a multiple-link type piston crank mechanism.
In order to vary a compression ratio between the volume in the engine cylinder with the piston at bottom dead center (BDC) and the volume with the piston at top dead center (TDC) depending upon engine operating conditions such as engine speed and load, in recent years, there have been proposed multiple-link type reciprocating piston engines each employing a multiple-link type piston crank mechanism (multiple-link type variable compression ratio mechanism) composed of three links, namely an upper link, a lower link, and a control link.
In a multiple-link type variable compression ratio mechanism, assuming that an angle (an inclination angle xcfx86 of an upper link) between an axial line of the upper link and an axial line of the direction of reciprocating motion of a piston pin center, becomes approximately 0xc2x0 nearby TDC, there are some drawbacks, for the reasons discussed below.
A piston side thrust force is dependent upon the inclination angle xcfx86 and combustion load, and thus an instantaneous energy loss based on a coefficient of friction between the cylinder wall (major thrust face) and the piston, piston speed, and piston side thrust force is also dependent upon the inclination angle xcfx86 of the upper link. Therefore, it is desirable to properly set the inclination angle xcfx86 in particular at a timing point that the product of piston velocity and combustion load becomes maximum after TDC on the compression stroke, from the viewpoint of reduced piston thrust face wear, reduced piston slapping noise, and reduced energy loss.
Accordingly, it is an object of the invention to provide a variable compression ratio mechanism of a reciprocating internal combustion engine, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a variable compression ratio mechanism of a reciprocating internal combustion engine, comprised of upper and lower links and a control link, which mechanism is capable of efficiently reducing energy loss during reciprocating motion of the engine, with a reduced inclination angle xcfx86 of the upper link with respect to an axial line of the direction of reciprocating motion of a piston pin axis, (that is, tan xcfx86), in particular at a timing point (or a crank angle) that an absolute value |Vxc2x7Wexp | of a product of a piston velocity V during downstroke of the piston and a combustion load Wexp becomes maximum.
In order to accomplish the aforementioned and other objects of the present invention, a variable compression ratio mechanism of a reciprocating internal combustion engine comprises a piston moveable through a stroke in the engine and having a piston pin, a crankshaft changing reciprocating motion of the piston into rotating motion and having a crankpin, a linkage comprising an upper link connected at one end to the piston pin, and a lower link connecting the other end of the upper link to the crankpin. At the top dead center position of the piston, when connecting points between the upper and lower links are able to be supposed on both sides of a line segment connecting the piston-pin center of the piston pin and the crankpin center of the crankpin, and the first one of the connecting points has a smaller inclination angle, measured in the same direction as the direction of rotation of the crankshaft, from the axial line of reciprocating motion of the piston-pin center and formed between a line segment connecting the piston-pin center and the first connecting point; as compared to the second connecting point, the first connecting point is set as the actual connecting point between the upper and lower links.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.